Restore the data block size to 62.
The former block size traded away good fit within cache lines in
order to gain faster division in deque_item(). However, compilers
are getting smarter and can now replace the slow division operation
with a fast integer multiply and right shift. Accordingly, it makes
sense to go back to a size that lets blocks neatly fill entire
cache-lines.
GCC-4.8 and CLANG 4.0 both compute "x // 62" with something
roughly equivalent to "x * 9520900167075897609 >> 69".
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index dc31cbc..26d8783 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -10,11 +10,14 @@
/* The block length may be set to any number over 1. Larger numbers
* reduce the number of calls to the memory allocator, give faster
* indexing and rotation, and reduce the link::data overhead ratio.
- * Ideally, the block length should be a power-of-two for faster
- * division/modulo computations during indexing.
+ *
+ * Ideally, the block length will be set to two less than some
+ * multiple of the cache-line length (so that the full block
+ * including the leftlink and rightlink will fit neatly into
+ * cache lines).
*/
-#define BLOCKLEN 64
+#define BLOCKLEN 62
#define CENTER ((BLOCKLEN - 1) / 2)
/* A `dequeobject` is composed of a doubly-linked list of `block` nodes.